try this: http://www.mediatek.com/en/downloads/usb-rt2870rt2770rt3x7xrt537xrt5572/
but not work for Yosemite
for yosemite you should try this: http://www.insanelymac.com/forum/index.php?app=core&module=attach&section=attach&attach_id=145582

sorry i'm not good for answering kernel panic issue..
If I got that issue, then i reboot the pc. I always use to boot with usb-hdd (usb bootloader) before the OS X can boot normaly from HDD
I think the problem are:
- BIOS setting (UEFI or EFI BIOS) you must google them to set up for different BIOS configuration of yours
- Bootloader costume for your system, I always uncheck GraphicsEnabler=No (coz my graphics card is ATI) then check Chameleon EFI not Chameleon Standard at Customize screen.
- I've got no clue for installing Yosemite on External IDE HDD. Sorry can't help...
According to your photo, I thinks you mus try to customize bootloader using Multibeast or Clover Configuration tool.

try this if you want to install niresh yosemite, this bootflags you must put on niresh yosemite menu bootloader for the 1st boot:
/amd1 graphicsenabler=No pcirootuid=0 npci=0x2000 -v
for 2nd boot after finishing 1st boot (if your HDD not boot properly, you still use USB niresh yosemite bootloader and select your HDD on menu):
-amd1 graphicsenabler=No pcirootuid=0 npci=0x2000
then after that you must use Chameleon Wizard to fix your bootloader so you can boot from HDD properly.

1st Quest: can you tell me more detail?
2nd Quest: No.
You can download the update from AppStore, but before that you must replace the Kext and mach_kernel with the same version with the update ver.
I suggest you to update with Combo package. like this http://support.apple.com/kb/DL1760

I have 2 step to upgrading from 10.9.0 to 10.9.5 (AMD processor)
- 1st step : for upgrading from 10.9.0 to 10.9.4 you must watch this
- 2nd step: using the same method like 1st step I only using this kernel (BSA_10.9.5_FX_rc1) for upgrade from 10.9.4 to 10.9.5
remember: before restarting computer, you must edit org.Chameleon.Boot.plist to add this on your bootloader
<key>Kernel</key>
<string>kernel</string>
or you can use Chameleon Wizard and check the Kernel part then write kernel name.
dont forget to use Kext Wizard for repairing permission.
(For Intel Kernel you can google it)